The bestselling story of Greece's bitter struggle against Italian occupation during World War Two, Captain Corelli's Mandolin, has become embroiled in controversy even as filming of the book gets under way on its island setting of Cephalonia.

Makers of the film, which stars Nicolas Cage, Penelope Cruz and John Hurt, have had to persuade anxious islanders that the blockbuster will be a love story, and will not reopen old wounds by concentrating on the brutal anti-fascist struggle and ensuing civil war.

Now the book's author, Louis de Bernières, has conceded that changes have been made to the Greek edition of the book because of fierce criticism of its portrayal of communist atrocities.

And, after accusations that he distorted history to portray the country's leftist partisans as 'dehumanised sadists', the author says he 'might be wrong'.

'After the writing of Corelli it became clear to me that many people were genuinely offended by the portrayal of the Communist Resistance, or simply thought that it was inaccurate,' de Bernières wrote yesterday in an email sent to The Observer. 'I haven't actually changed my mind about what I think is the truth, but I had to bear in mind the possibility that I might be wrong.'

The book describes a love triangle between a member of Greece's communist Resistance movement, an officer in the Italian occupying force on Cephalonia, and Pelagia, the beautiful daughter of the local doctor. It includes accounts of communist atrocities against their right-wing foes during the civil war that followed Italy's occupation.

Only last year the soldier-turned-writer issued a blistering assault on the tiny circulation Morning Star for accusing him of promoting crude anti-communism in the book. 'How long are you people going to sit in the dark in an air pocket, wanking each other off? Your ship has sunk, brothers. It was historically inevitable and just now the historical conditions have been fulfilled. Goodbye to the biggest failure and disappointment since the non-return of Christ,' he wrote.

Now his views appear to have mellowed. Yesterday he said: 'The story of the Resistance is extremely complex, and whereas the communists massacred entire villages in some places, I understand that in others they set up drama classes.'

De Bernières's account of the changes he has made to the Greek version of his book mirrors the efforts British film-makers have made to reassure the citizens of Cephalonia (also known as Kephalonia) about their plans. One prominent politician conceded that many did not want the book filmed on the island at all. 'There was a lot of under-the-table negotiations to have the film take place on Cephalonia,' said Gerassimos Apostolatos, a distinguished former Conservative MP from the island.

'All over our island there were cases of real-life Corellis and Pelagias, but the book is also full of things that really offend,' said Gerassimos Artelanis, mayor of Sami where much of the movie is being filmed. 'So we set up a committee of historians working alongside all the island's mayors and decided the British film company would have to confirm that what they were making was a love story and not a political story... because you know not even we Greeks have decided who was right and wrong during the civil war. It's still a bitter thing.'

The British film-makers confirm the delicacy of their negotiations. 'It is true the local prefect asked us for assurances that the film would not touch on Greece's brutal civil war,' said Kevin Loader, one of three British producers. 'We had no problem doing that because it was always going to be a love story and nothing else,' added Loader, whose London-based Working Title Films counts Four Weddings and a Funeral among its box-office draws.

De Bernières said yesterday: 'It was never part of the purpose of Corelli to stir up bad blood. Corelli is about other themes, and I wouldn't want the book to be distorted for Greek readers, which is why I agreed with my publishers and translator that some of my language and opinions should be moderated. The Greeks don't need some foreigner sticking his oar in when they can, and do, perfectly well argue among themselves.'

Although the author says 'nothing was actually cut', the novel was amended to placate a potentially hostile audience prior to its publication in Greece in 1995.

Several offending passages have been excised altogether. Greek readers who turn to chapter 63, for instance, are not told that 'the communists began to deport awkward characters to concentration camps; from a safe distance they had watched the Nazis for years, and were well-versed in all the arts of atrocity and oppression.' They do not read that 'Hitler would have been proud of such assiduous pupils'.

Nor do they see the author's note, which was published in the early English language editions of the book and appears in other foreign editions. It is in the note that de Bernières berates the 'disconnected intellectual' who has traditionally tried 'to maintain that the Greek communists were romantic heroes who were unjustly oppressed by the imperialist and duplicitous British, in order to restore the monarchy against the will of the people'.

'I have tried to be as true to history as possible,' he writes. 'I have been unable to conclude otherwise than that, when they were not totally useless, perfidious and parasitic, they were unspeakably barbaric.' With such snippets removed, the novel was initially well received in Greece where one critic wrote that a 'Greek could not have written better'.

Over 25,000 copies have been sold since Psichogios, the Athenean publishing house, first printed it in 1995. It is now being flagged as a 'Hymn to our Homeland'.

In the giant film-set that is Sami, the word is out that the British author may soon be visiting. Those thankful for the book's impact on local tourism have already implored the mayor to make him an honorary citizen. 'But you know,' said Mayor Artelanis, 'what I would really like to ask him is where he got all his information from. If they turn it into a political film, then we will take measures.'

'You can be sure that we will take the issue to the international court of justice at the Hague. We will fight it all the way. For us Captain Corelli must be what it is very good at - a love story from beginning to end.'

The low-down on the Captain

Author: Louis de Bernières

First published: 1994

Pages: 434

Price: £6.99 (Vintage pb)

Position in bestseller list: 92nd

Weeks in list: 234

Copies sold: 1.5 million

Number of final chapters: two - de Bernières added a final final chapter in 1998

Plot: Italians occupy Greek island of Cephalonia during Second World War. Doctor's daughter and fisherman lover support local resistance. Enter Captain Corelli (with mandolin) to organise occupation. Captain falls in love with doctor's daughter. Savage war brings invaders and defenders together. Mandolin gets lost. War ends. Captain leaves. Not going to tell you the rest.

Prize: 1995 Commonwealth Writers' - first British novel to take the award.

What they said:

'Satirical and earnest' (Observer)

'Absolutely brilliant' (Jeremy Paxman)

'Book of the crudest and most brazen anti-Communism' (Morning Star - de Bernières responded: 'Your ship has sunk, brothers... It was historically inevitable' but has since conceded that 'the story of the resistance is extremely complex'.)

'The story was not told in proper order. It kept jumping about too much.' (member of Sowerby Bridge Afternoon Readers' Group)